The invention relates to counters, and more particularly, to counting circuits applied in distance estimation for ultra wideband (UWB) application.
In the ultra wideband (UWB) physical layer (PHY) specification V1.0 proposed by Multiband orthogonal frequency division multiplexing (OFDM) SIG of WiMedia, “ranging and location awareness” is included. This function is targeted to measure the distance between two UWB devices with accuracy and precision of 60 cm or better. One 32-bit ranging timer with minimum clock rate of 528 MHz is required to measure the timing difference between frame transmitting from one device and is received at another device. The maximum clock of this ranging timer is up to 4224 MHz, and is thus difficult to implement, with clock rate from 528 MHz to 4224 MHz the most critical part.
In UWB systems, the relative distance between two devices can be measured, for example, estimated by multiplying the speed of light by the measured propagation delay between the two devices. In order to support this “ranging” function, one 32-bit binary counter, ranging timer is required. Necessary clock rate is from 528 MHz to 4224 MHz with precision of 60 cm or 10 cm. With increased clock rate, precision of the ranging function improves. Conventionally, a binary counter is used to implement ranging timer, as disclosed in patents U.S. Pat. Nos. 5,682,342 and 6,690,525. Some approaches minimize the critical path of the binary counters to increase the clock rate of the counter, such as those shown in FIGS. 1A and 1B.
However, even with currently popular 0.13 um or 90 nm CMOS process, such “binary” or “Gray code” counters have difficultly meeting the speeds over 4 GHz, according to standard-cell library design flow.